Evaluation of biochemical responses of bean species (Phaseolus ssp.) to high temperature stress

Heat stress caused by climate change have profound implications from germination to maturity including vital physiological and biochemical processes in plants. Heat associated traits in bean species (Phaseolus spp.) is crucial due to the anticipated rise in heat stress frequency and intensity driven by climate change. A total of 196 bean genotypes comprising common bean (P. vulgaris L.), tepary bean (P. acutifolius L.), scarlet runner bean (P. coccineus A. Gray), year bean (P. dumosus Macfady), and lima bean (P. lunatus L.) were assessed for agro-morphological traits under moderate heat stress (field) and extreme heat stress (glass greenhouse) conditions. According to a two-year selection in field and greenhouse, eight notable heat-tolerant genotypes of P. vulgaris, P. acutifolius, P. coccineus, P. lunatus and two heat-sensitive genotypes (P. vulgaris) were compared for the endogenous accumulations of abscisic acid (ABA), jasmonic acid (JA), salicylic acid (SA), chlorophyll contents (CC), and maximum quantum efficiency of photosystem II (Fv/Fm) under heat-stressed and non-stressed conditions. Although most genotypes of P. acutifolius (G182), P. lunatus (G192), and P. coccineus (G192) were selected as heat-resistant, a few genotypes of common bean (G50, G43, G116, G138, and G123) exhibited to be heat-tolerant under moderate heat stress and extreme heat stress conditions. Biomass, Fv/Fm and CC had significant direct effects on heat stress resistance scores. Under heat-stressed conditions, the endogenous accumulation of ABA, JA, and SA was significantly higher compared to non-heat-stressed conditions, indicating their role as survival strategies. Conversely, CC and Fv/Fm were higher under non-stressed conditions. Notably, heat-sensitive genotypes generally exhibited higher accumulation of JA and SA than that of heat-tolerant genotypes under non-heat-stressed conditions, suggesting distinctive coping mechanisms. These findings emphasize the adaptive characteristics of heat-tolerant bean genotypes, such as P. acutifolius, acquired during their evolutionary history prior to domestication.